MetalMagus Posted November 22, 2011 Share Posted November 22, 2011 Hi Hope someone on the forum can help me diagnose an issue I have with a VDO rev counter I have fitted to my 200 TDI Defender 90. The rev counter works fine up to approximately 3000 RPM. Indicates correctly with a blip on the accelerator pedal. Once you reach 3000 RPM which equates to around 65 MPH then the rev counter dies and drops to zero. Now I don't do this kind of speed very often but I noticed it the other day on a down hill wind behind me run. Once the revs reduce the rev counter springs back into life. The rev counter gets the signal from the "W" terminal on the alternator so I'm wondering if either my alternator is slipping above 3000 RPM, but I cannot hear any screeching from the belt, or if the alternator is stopping outputting over 3000 RPM. Any ideas? Cheers Sean Quote Link to comment Share on other sites More sharing options...
landroversforever Posted November 22, 2011 Share Posted November 22, 2011 My first thought would be to check the condition of the belt and the tension. I had it on mine that it was slow to catch up with the revs and over about 2k rpm it wouldn't get much faster. Belt was shredded and loose. Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted November 22, 2011 Share Posted November 22, 2011 My first thought would be to check the condition of the belt and the tension. I had it on mine that it was slow to catch up with the revs and over about 2k rpm it wouldn't get much faster. Belt was shredded and loose. Doesn't sound that likely as Sean said his rev counter drops to zero when he goes over 3000rpm, if it was just slipping then it would stay steady or creep up/down. I'd place bets on it being something electrical breaking down, whether it be in the rev counter or alternator I don't know. Any chance of testing it on another alternator? Quote Link to comment Share on other sites More sharing options...
mmgemini Posted November 22, 2011 Share Posted November 22, 2011 Are the connections clean and tight at the "W" terminal ? Quote Link to comment Share on other sites More sharing options...
jad Posted November 22, 2011 Share Posted November 22, 2011 I was having trouble with my alternator recently. Tacho was all over the place, also had all lights pulsing as the voltage was bouncing between 14-16 volts. turned out to be a nut under where the positive terminal bolts on was loose, it never stopped charging though, assume u dont have any other symptoms but thought it might be worth mentioning.... Quote Link to comment Share on other sites More sharing options...
SORNagain Posted November 22, 2011 Share Posted November 22, 2011 I believe that some rev counters with a wide sweep often have two coils mounted at 90 degees to one another, and a magnet on the needle shaft. The RPM is converted into a voltage in the normal way, and one coil is fed with the sine of this voltage and the other with the cosine. This gives a linear wide sweep which would be impossible to achieve with the normal moving coil and spring arrangement found in conventional meters. Sounds like one of your coils is not working for some reason.... Quote Link to comment Share on other sites More sharing options...
western Posted November 22, 2011 Share Posted November 22, 2011 maybe it's just not reading the incoming signal from the alternator W terminal, if the 3 slider switches on the rev counters rear face are not set then the rev counter will show a incorrect reading, I have a similar rev counter on my 200tdi, the 3 slides are numbered 1,2,3. put 1 & 3 up & 2 down, if moving the sliders doesn't make any difference, the rev counter may be faulty. Quote Link to comment Share on other sites More sharing options...
Tanuki Posted November 22, 2011 Share Posted November 22, 2011 Alternator brushes? If they're worn and making poor contact at higher RPM, they could be generating a waveform at the alt's "W" terminal that the revcounter can't handle. --Tanuki. “One dollar can save a life - the opposite must also be true!" Quote Link to comment Share on other sites More sharing options...
MetalMagus Posted November 22, 2011 Author Share Posted November 22, 2011 Thanks for all the feedback gents. Gives me things to check and go through. Probably start off at the alternator and work my way back. Will let you know how I get on. Now all I need is some daylight and my day job not to get in the way. Cheers Sean Quote Link to comment Share on other sites More sharing options...
MetalMagus Posted December 6, 2011 Author Share Posted December 6, 2011 Okay sorry for taking so long to update. The verdict is in. A loose alternator belt and a very polished alternator pulley. Belt now screeches when cold and the rev counter doesn't spring to life until things have warmed up a little. Is there an "easy" way to adjust the alternator to give me belt tension? Work and lack of daylight keep preventing me from getting under the bonnet and fixing this. Plus it's blumming freezing. How I envy people with a garage. Can I get to it from underneath easier, or do I need to remove the air filter and intercooler pipes. If I can nurse it along until the weekend then I may get it fixed. Cheers Sean Quote Link to comment Share on other sites More sharing options...
landroversforever Posted December 6, 2011 Share Posted December 6, 2011 There should be an adjuster for the position of the Alternator, that will tension the belt Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.